Electronic control system for direct-current motors



y 1950 J. G. HANEIKO 2,516,568

ELECTRONIC CONTROL SYSTEM FOR DIRECT-CURRENT MOTORS Filed May 5, 1948 WITN ESS ES:

(25a W/j/ INVENTOR J'a/vr; 6, Hana/K0.

CA 'W ATTORN EY Patented July 25, 1950 ELECTRONIC CONTROL SYSTEM FOR DIRECT-CURRENT :MOTORS John G. Haneiko, East Aurora, Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania.

Application May 5, 1948, Serial-No. 25,1 55

1 Claims. (coals-331) "My-invention relates to electronic systems for energizing a'direct-current motor from an alternating-current source to run at controllable speed.

"It-is an object of the invention to'improve and simplify suchsystems as regards their IR-drop compensating components and performance, 1.0. as regards-those circuits and-devices of the system thatstabilize undesired variations of the motor speed due to changes-in motor armature current as-may be caused bychanges in theload or torque requirements of the-motor.

In the known electronic control systems of this kind, current is supplied to the armature of a separatel excited direct-current motor from an alternating-currentsource through a controllable rectifier. As a-rule, a pair of rectifyingtubes of the gaseous-typesuch -as thyratrons or ignitrons, are arranged to conduct current .to the armature in successive half-periods of alternating current voltage. The amount of current supplied to --the :armature depends upon the instant at which the conduction through. the rectifier tubes is :initiatedrelative to the half-period of the source in which. the tube is capable of. conducting. To controlthe -.-firing point,.each rectifier tube has a control, circuitimpressed by .variable control voltage. .-As.a rule, the control voltageisthe resultant of an alternating-voltage component. of fixed magnitude .and a given-phase displacement relative to the voltage of the alternating-current source land-ofea secondcomponent; voltage which is unidirectional and otvariable magnitude. The uni-directional control .voltage is made up primarily of a substantially constant component and avariable component derivedafrom an auxihary directecurrent source through ,a master control tube. The master-control. tube is so. connected that the magnitude of the variable component voltage depends upon the conductivity of the. master, control tube. For purposes of speed regulation, the. conductivity of the master control tube isvaried in accordancewith the setting of a speed control rheostat as well .as in. accordance with-the armaturevoltage and the armature current-of the motor.

In-theknownsystems, only. .the just-mentioned componentv control voltages. proportional to the motor armature .voltage and the. control voltage determinedby-the setting of=the speed control rheostat are. directlytapplied to:the gridcircuit, while the control voltage proportional to the armature current is applied to the grid circuit through .an electronic arrangement, which includes an auxiliary vamplifiertube. The plate circuit-of the auxiliarytube is energizedirom a separate source or direct-current voltage and its grid circuit is controlled by signal voltage derived from the armature circuit of the motor.

,I t is a more specific object of my invention to simplify control systems of the type above referredto byeliminating the auxiliary amplifier tube andthe appertaining tube circuits for applying the current responsive grid voltage to the mastercontrol tube of the system, thus reducing the number of system components and the cost of the equipment while also facilitating the adjustment of the control system.

Another more specific object of the invention is to design the supply means of the currentresponsive grid voltage for the master control tube in suchamanner as tosecure a high stability of this component grid voltage.

'Inorder toachieve these objects, systems according totheinvention are designed as set forth in theannexed claims and apparent from the following description of the two motor control systems e gemplified by the circuit diagrams shown in Figs. 1 and 2, respectively, of the drawing.

{The alternating current terminals I of the con trol system shown in Fig. 1 are connected to the primary 2 of.,a,power transformer 3 whose main secondary windings has a tap 5 located in the midpositionbetween the terminals '5 and l of the ;winding. Transformer 3 is equipped with two additional secondaries 8 and 9.

Thearmature II and a series field Winding 52 otnlotor lVi areconnected to the tap point 5 in .seriesrelation to each other. The main field winding 130i the motor is separately energized by substantiall constant voltage through a rectifier M from the secondary 8 of transformer 3. .TwoQrectifier tubes l5 and [6, for instance thyratrons, have their respective anodes connected to theterminals] and 6 of the transformer secondaryfi inseries with the respective primary windings ll and .IB of a transformer 89 whose secondary ,2! base center tap 22. The control Bleotrodes or grids 23 and 24 of respective tubes [Sand .[6 are connected through series resistors .25 and lii .acrossacenter-tapped secondary 2? of a1phase shifttransformer 28 whose primary 2 9 is. connected through a phase shift circuit ti with, an appertainingtransformer 32 to the secpndary; 9 of the power transformer 3.

The tubes l5 and i6 have a common cathode lead v,"titwhich forms part of the motor armature .circuit. Two resistors 33 and 34 are connected in seriesv with each other across the motor armature'i I. ,A circuit point between resistors 33 and .a i isconnectedthrougha-lead 35 to the slider 3 35 of a speed control rheostat SR whose resistor 37 is connected across a suitable source 38 of constant direct-current voltage in series with two resistors 39 and M. Resistors 39 and M are also series-connected with a resistor 42 which is disposed in the plate circuit of a master control tube t3. This plate circuit is energized from the constant voltage source 38 and includes also the above-mentioned resistor 31 of the speed control rheostat SR.

Tube 63 is a vacuum tube and may consist of a pentode, as shown. Its control grid 44 is connected through a resistor 45 and a resistor 46 with the slider or tap point 41 of a p'otentiometric rheostat .8. One terminal of rheostat 48' is connected to the tap point 22 of the secondary winding 2| of transformer 19. Theother terminal of rheostat :8 is connected to the cathode 49 of a twin diode 58 or the like rectifying apparatus. The two anodes SI and 52 of tube 50 are connected to respective terminals 'ofthe secondary 2|. A load resistor 53 is connected across the secondary 2|.

The magnitude of current applied to the armature H of motor M depends upon the average conductance of the rectifier tubes I5 and it and hence" on the firing point of these tubes. This firing point is conof the rectifier tubes it and 16. Besides, this voltage is substantially cancelled by the voltage from 1 rheostat 31.

the rectified voltage and trolled by the control potential impressed between the cathodes and control electrodes, respectively, of the rectifier t'ubes'by means of appertaining control or grid circuits.

The control circuit for tube it; extends from grid 23 through resistor 25 and one-half of the secondary winding 2'5 of the phase'shift transformer 28 to the center tap of winding 27. The grid circuit for tube It extends from grid 24 through resistor 2b a'ndthe'other half of secondary winding 21 to the samece'nter tap. From then on, both grid circuits extend through resistor 42, resistor 41, resistor 39, part of'resistor 3'! to the slider '36 ofthespeed control rheostat SR, thence through lead'35 and resistor 34 to the common cathode lead 38 of the tubes l5 and Hi. This control circuit of tubes l5 and IE is impressed by five voltages, as explained presently.

The secondary 2'! of phase shift transformer 28 provides the control circuit'with an alternating voltage of the same frequency asthateffective across the secondary winding 4 of the power transformer 3, but the'phase of the alternating voltage impressed on the grid circuit is displaced by the phase shiftj circ uit 3!, preferably so that it lags 90 behindthe voltage of secondary winds A constant direct-current voltageis' impressed on the rectifier control circuit across the resistors 3S and 4 i. This constant voltage results from the voltagedrop caused in these resistors by the current from source'38. The polarity of the volt age across resistors 39 and M tends to make the control grids 23 and 2 4 of rectifier tubes l5 and [6 positive with respect to the cathodes. Another direct-current voltage is applied to the grid circuit from across the resistor '42. The magnitude of this voltage depends upon the conductivity of the master control tube 43 and varies in dependence upon the-voltage conditionof the appertaining grid circuitin the manner explained in a later place.

A unidirectional voltage, effective in the grid circuit of rectifier tubes 15 and It; appears'also across the tapped-01f portion of resistor 31 between slider 36 and the point of attachment to resistor 39. This-voltage depends upon the ad- It followsirom the foregoing that the resultant grid-cathode voltage applied to the rectifier tubes 15 and I6 is primarily comprised of the phase shifted alternating voltage supplied through transformer 28, the constant unidirectional voltage supplied by resistors 39 and M, and the variable unidirectional voltage supplied by the resistor 42. These three voltages are so proportioned that when the master control tube 43 conducts maximum current, the negative potential caused by the voltage across resistor 32 (first resistor) is of such a magnitude as to prevent the resultant grid-cathode potential of the rectifier tubes from rising above the critical value necessary to ren der the rectifier tubes conductive. If the conductivity of the master control tube 43 decreases, the resultant grid-cathode potential impressed on the rectifier tubes l5 and I6 rises above the critical value so that the firing point of the rectifier tubesis advanced and causes these tubes to conduct an amount of current through the motor armature which increases with decreasing conductivity of the master control tube.

The conductivity of control tube 43 depends upon the grid-cathode potential applied to this tube by the appertaining grid circuit. The grid circuit can be traced from grid 44 through resistor and resistor 56 to a tap point 81 of rheostat &8, and through the tapped portion of rheostat 48, lead 55,. resistor 34 and lead 35 to the slider 36 of speed control rheostat SR, and thence through the tapped portion of resistor 31 to the cathode lead 56 of control tube 43. This grid circuit is impressed by three voltages whose re- 1sultant efiect determines the grid cathode potenial.

The first grid voltage is provided by the portion of resistor 37 tapped ofi by the slider 36 in speed control rheostat SR. This voltage and consequently the selected adjustment of the slider tlldetermine the speed at which the motor M is intended to run.

{mother voltage is impressed on the grid circuit of control tube 43by the resistor 34 (second resistor). As mentioned, this voltage varies in proportion to the armature Voltage of motor M. The polarity of this variable voltage opposes that of the above-mentioned control voltage derived from the speed control rheostat SR.

A third-voltage is impressed on the grid circuit of control tube 63 from the tapped-off portion of rheostat 48 (third resistor) between tap 4i and lead 55. This third voltage is supplied through the rectifier 5tlfrom the transformer I9. Since transformer 19 is energized by the motor load current flowing through the rectifier tubes l5 and it, the rectified voltage across rheostat 48, and hence the voltage impressed on the grid circuit of the control tubev i3 varies in proportion to the armature current and is a measure of vIR drop in the motor. armature circuit.

-Disregarding for a moment the eifect of the last-mentioned voltage fromrheostat 48 and as:

shining: that the .load .or .torique :ofsmotorrM :remains constant, .the conductivity 'Of the gmaster control tube :43,- randzthcreforer the ifiringxpointof the :rrectifier tubes 2 i :-:and l6, :and :the speed :of thermotorv:M-.-are ideterminedeonlyby the, selected settingaofthe control rheostat SR. As the adjustable .tapa-firt is moved. away .from'the end: of 2 the resistor :31. connected. tolead: 56,: the speed :of the moto .:.is 1 increased. If the I'torque varies, ,:the armature voltage varies-accordingly, andso does the voltage impressedromtheigrid circuit of control-tube fromacross theresistor 34. fi'lhevpolarity 1 of the voltage across resistor 34 is such that an increase in torque acts through resistor E l to' decrease the conductivity or the mastercontrol "tube- 43 in order: to -advance the firi-ngz point ofthe. rectifier tubes [5" and f6. Conversely, the voltage across resistor "-34 causes the-grid circuit of control tube 43: todelay thefi'ring point of rec tifier tubes s l5 and 16- inresponse to---a' decrease in-torque. '--In this manner, the-system compen sates for variation'in armature voltage clueto variations in load.

The above-mentioned third "voltage impressed on the 'grid circuit of control tube 43 from resistor 58 (third resistor) acts cumulativelywith respect to'the adjusted voltage from speed control'rheo'stat SR, and in this manner compensates for variations of the armature voltage due to the IR. idrop in'the armature circuit. If the loadcurrent increases andcauses the motor speed to drop from'the' desiredvaluedue tothere'ducing effect'ofthe'lRdrop on the armatureterminal voltage, the rectifying voltage impressed through tube 5-3 across the potentiometer "resistor"48 increases. As "a'result, the "grid circuit behavesas if the speedcontrolvoltage adjusted at the rheostat SR'Were slightly increased, and the'firing point ofithe rectifier tubes I5 and I6 is shifted to increase the armature voltage of the motor an amount suificient to compensatefor IP.--drop responsive speed variations.

Itiw'illbe recognized that inthe above-described controlsy'stem the grid voltage that measures the IRdropofthe motor armature circuit and ap-- pearsacrossthe resistor 48 .is'not, supplied from a separate-source through an amplifiertube but is. caused by the motor armature. current itself. In this manner, the additional amplifyingv equip ment heretofore used for this. purpose is eliminatedeand the design and adjustment of the systemias .a whole-correspondingly simplified.

Due' to .the'fact that: the current;measuring component grid voltagefor the vcontrolitube 45 is.caused..by thezrectifier armature current, the sometimes appreciable irregularitiessof thiscurrent-may be transferred into the gridacircuit of thecontrol tube and may affect the stabilitycf the control voltage across resistor 42 thusaffectin theaccuracyz of the control performance.

. Ina a system'.accordingu t0 the) invention, I howevergsuch disturbingeffects are minimized by the periormanceof theresistonlfi series connected to the sliderd'l of the potentiometric rheostat', in conjunction with atcapacitorJGO' which, is series connected with the,-resistor=46 across the tapped off portionof the *rheostat -48. When a rapid voltage change occursiacrossthe tappedoitportion:of rheostat 48, .thecapacitorfill varies its chargeand passes a-charging or .dischargingcurrent throughttheloop circuit. formed by resistor 46 and the-active portionof-rheostat48. This capacitive current. impresses. onthe loop circuit moltagewiththe efiect of minimizing. the.;cause of 1 the disturbing voltage .change. Eor; instance, any sudden rrise in rvoltageyacross rheostats .58 causes a flow of current through the capacitor 50 (during :the interval .of voltage change. This current produces across the resistor 46 a voltagewhi-chsgmakes-the grid of the grid A l-more positive ;-relative :to the cathode and thereby changes .the' voltage drop .,-across resistor- 42 .with the. effect-of delaying; the firing of rectifier tubes l'5iandl6. Asa result, the vcurrent:through the armaturezcircuit isreduced to the extentrequired iorzpreventingzthe rise in voltage. across rheostat 48.

".Thei motorqcontrol system shown inFig. 211's largely similar -lt0 thatacccrding to Fig. 1; and represents ;a.mo dification of .the circuit means which-:connectsthe grid circuit. Of. the mastercontnol -tube 43 with. the smotor armature circuit, for deriving from the .latter a voltage propor tional to the :-IR dropxin the armature circuit. Circuit elementsiof the: modified system shown Fig. :2 thatcorrespond to elements of. Fig. lare denoted by the same respective reference characters. Since the:'performance' of thesystem of Fig. :2 as a whole is similarzto that of the system.previously described, the following description is limited" to the modified features.

The essential difference of thesystem shown inFigJZirom that ofFig. 1 consists in the fact that. the rectifier-tube 50 and the transformer 1-9 of Fig. l are eliminated. The armature circuit includes a low ohmic series resistor 5 I The voltage drop across'resistor 5i is proportional to the armature current and hence a measure of the IR drop. The grid circuit ofthe control tube 43 extends 'irom'control grid ltthrough resistors 45, EL MQGS, to the speed-control rheostat 31, then-back to the cathode of tube 53. The voltage drop across resistor is proportional to th armature voltage and opposed to the voltage taken from resistor 6L Consequently, the resultant voltage impressed across the series-arrangement of resistors'fil and 33 corresponds to the differentialvalue of motor terminal voltage and IR drop. By properly proportioning the ratio of the two voltage drops, the resultant voltage can be made proportional to the counter E. M. F. of the motor which is substantially proportional to the motor speed. More in detail, with increase in armature current, an increasing negative voltage is applied .from resistor 6! to the grid of tube 43. As a result, the voltage across resistor 34 is reduced and the firing, angle oi thyratrons I5, i6 is advanced. The .portionof armature voltageacross resistor 34 approximately balances the voltage across the efiective portion of rhesotat 31. As a rule, the voltage-across resistor 34 may. be about one-fifth of the total armature voltage.

Resistor-=46. andcapacitor 60 and resistor 66 forma stabilizingcircuit, and capacitors 59 and 62 serves as filters. As long as the armature voltageis stable, no voltage is impressed across resistor .46. In the event of asudden change in armature current and voltage, a corresponding change appears in the voltage drop across resistor 33- sothat the. capacitor 60 varies itscharge and impresses avoltage across resistor 46 which is effective in the grid circuit of tube 43 in the same stabilizing manner as explained above Withrefera ence to. capacitor 60 and resistor 46 in Fig. 1.

=It will be understood by those skilled in theart thatesystems-according. to the invention can ,be modified in various respects without departing from the subjects andessence of the invention and within the essential features of the invention set forth in the claims annexed hereto,

I claim as my invention: i r 1. An electronic motor control system, comprising alternating-current supply means, a directcurrent motor, a controllable rectifier tube seriesconnected with said motor across said supply means and having a control circuit with voltage supply means for controlling the current rectified by said tube and traversing said motor, said voltage supply means including a first resistor, a control tube having a plate circuit extending through said resistor to impress thereon a variable voltage and having a grid circuit for controlling said variable voltage, adjustable directcurrent supply means connected with said grid circuit to impress thereon an adjusted voltage in accordance with a desired motor speed, a second resistor disposed in said grid circuit and connected across said motor to apply to said grid circuit a variable voltage in accordance with the motor terminal voltage and in oppositon to said adjusted voltage, circuit means series-connected with said motor and said rectifier tube to be traversed by said current and having athird resistor for developing a voltage drop caused by said current,.a fourth resistor and a capacitor connected in series with each other across said third resistor, and said third and fourth resistors being series-connected with each other in said grid circuit to pro: vide IR-drop compensating voltage for said grid. circuit.

2. An electronic motor control system, comprising alternating-current supply means, a directcurrent motor, a controllable rectifier tube seriesconnected with said motor across said supply means and having a control circuit with voltage supply means for controlling the current rectified by said tube and traversing said motor, said voltage supply means including a first resistor, a control tube having a plate circuit extending through said resistor to impress thereon a variable voltage and having a grid circuit for controlling said variable voltage, adjustable direct current supply means connected with said grid circuit to impress thereon an adjusted voltagein accordance with a desired motor speed, a second resistor disposed in said grid circuit and con nected across said motor to apply to said grid circuit a variable voltage in accordance with the motor terminal voltage and in opposition to said adjusted voltage, a transformer series-connected with said motor and said rectifier tube, a third resistor, a rectifier having an input circuit connected across said transformer and an output circuit connected across said third resistor, and said third resistor being connected in said grid circuit to provide it with corrective voltage for IR-drop compensation.

v 3. An electronic motor control system, comprising alternating-current supply means, a direct-current motor, a controllable rectifier tube series-connected with said motor across said supply means and having a control circuit with voltage in accordance with a desired motor speed,

second resist-or disposed in said, grid circuit a d s connected across said motor to apply to said grid circuit a variable voltage in accordance with the motor terminal voltage and in opposition to said adjusted voltage, a transformer series-connected with said 'motor and said rectifier tube, a third resistor, a. rectifier having an input circuitconnected across said transformer and an output circuit connected across said third resistor, a fourth resistor and a capacitor connected in series with each other across said third resistor, and said third and fourth resistors being series-connected with each other in said grid circuit to provide IR-drop compensating voltage for said grid circuit. I

4. An electronic motor control system, comprising alternating-currentsupply means having a transformer winding with two terminal points and a mid-point, a separately-excited direct-current motor having an armature, two controllable rectifier tubes plate-connected to said respective terminal points and having a common cathode lead connected to said midpoint in series with said armature, said rectifier tubes having respective control circuits having a common circuit portion and voltage supply means for controlling the current rectified by said tubes, said voltage supply means including a first resistor disposed in said common circuit portion, a control tube having a platecircuit extending through said resister to impress thereon a variable voltage and having a grid circuit for controlling said variable voltage, adjustable direct-current supply means connected with said grid circuit to impress thereon an adjusted voltage in accordance with a desired motor speed, a second resistor disposed in said grid circuit and connected across said motor to apply to said grid circuit a variable voltage in accordance with the motor terminal voltage and in opposition to said adjusted voltage, a rectifier, a transformer having two primaries series-connected between said rectifier tubes and said terminal points respectively and having a secondary connected to said rectifier, said rectifier having an output circuit provided with a third resistor, and said fourth resistor being connected in said grid circuit to impress thereon a corrective voltage for IR-drop compensation.

5. An electronic motor control system, comprising alternating-current supply means having a transformer winding with two terminal points and a tapped midpoint, a separately-excited direct-current-motor having an armature, two controllable rectifier tubes plate-connected to said respective terminal points and having a common cathode lead connected to said midpoint in series with'said armature, said rectifier tubes having respective control circuits having a common circuit portion and voltage supply means for controlling the current rectified by said tubes, said voltage supply means including a first resistor disposed in said common circuit portion,- a control tube having a plate circuit extending through said resistor to impress thereon a variable voltage and having a grid circuit for controlling said variable voltage, adjustable direct-current supply means connected with said grid circuit to impress thereon an adjusted voltage in accordance with a desired motor speed, a second resistor disposed in said grid'circuit and connected across said motor to apply to said grid circuit a variable voltage in accordance with the motor terminal voltage and in opposition to said adjusted voltage, a rectifier, a transformer having two primaries seriesoonnected between said rectifier tubes and'said terminal points respectively and having a sec-.

ondary connected to said rectifier, said rectifier having an output circuit provided with a third resistor having a tapped-off portion, a fourth resistor and a capacitor series-connected with each other across said portion, and said fourth resistor being series-connected with said portion in said grid circuit to impress thereon an IR-drop compensating voltage cumulative to said adjusted voltage.

6. An electronic motor control system, comprisin alternating-current supply means, a direct-current motor, having a separately excited field Winding and an armature, a controllable rectifier series-connected with said armature across said current supply means and having a control circuit for controlling the rectified current traversing said armature, a control tube having a plate circuit with a load resistor, said load resistor being connected in said control circuit to impress thereon a variable voltage, said tube having a grid circuit for controlling said variable voltage, adjustable direct-current supply means connected with said grid circuit to impress thereon an adjusted voltage in accordance with a desired motor speed, a first resistor series-connected with said armature, a second resistor connected across said series connection of armature and first resistor so as to be impressed by voltage substantially proportional to the motor speed, said second resistor having a portion connected in said grid circuit to impress thereon a variable grid voltage in opposition to said adjusted voltage, a third resistor seriesconnected with said portion in said grid circuit, and a capacitor series-connected with said third resistor across at least part of said second resistor for stabilizing said variable grid voltage.

7. An electronic motor control system, comprising alternating-current supply means, a direct-current motor, a controllable rectifier tube connecting said motor to said supply means and having a control circuit with voltage supply means for controlling the motor speed, said voltage supply means including a first resistor, a control tube having a plate circuit extending through said resistor to impress thereon a variable voltage and having a grid circuit for controlling said variable voltage, adjustable direct current supply means connected with said grid circuit to impress thereon an adjusted voltage component, a second resistor connected with said motor for providing a voltage drop proportional to an electric condition of said motor and connected in said grid circuit to impress thereon a variable grid voltage component, a third resistor series-connected in said grid circuit, and a capacitor, said third resistor and part of said second resistor being connected in series relation to each other across said capacitor for stabilizing said variable grid voltage component.

JOHN G. HANEIKO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,312,117 Moyer et a1. Feb. 23, 1943 2,400,599 Reeves May 21, 1946 2,422,567 Puchlowski June 17, 1947 

